In a jet engine, a shaft is formed in a hollow shape, and a center bent tube may be provided inside the shaft. In the center bent tube, a bearing or the like which supports the shaft is connected to external air, the tip portion of the center bent tube is fixed to the shaft, and the center bent tube rotates along with the shaft.
Patent Documents 1 and 2 disclose jet engines which includes the center bent tube. Patent Documents 3 and 4 disclose a piston ring which slides on a cylinder related to sliding components disclosed in Patent Documents 1 and 2.